Planetary News: Venus (2006)
A Vortex Spins Around Venus' South Pole
By Emily Lakdawalla
June 27, 2006
The European Space Agency today released several sets of images from Venus
Express' first orbit around our sister planet, including a movie showing a
cloud structure spinning around Venus' south pole. The Visible and Infrared
Thermal Imaging Spectrometer (VIRTIS) captured the data between April 12 and
April 19, as the spacecraft swept out a very long initial orbital path that
took it 350,000 kilometers (220,000 miles) below the south pole.
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A week of weather over Venus' south pole
On its first orbit of Venus, Venus Express swung out to more than
350,000 kilometers (220,000 miles) distance and was able to encompass
the entire globe in one VIRTIS field of view. Over seven days, it watched
a two-lobed vortex swirl around Venus' south pole. The images were captured
at an infrared wavelength of 5 microns. At this wavelength, Venus' atmosphere
reflects solar radiation (bright yellow dayside of Venus, at the bottom
of the image). At this wavelength there is also heat emanated from the
hot atmosphere at about 60 kilometers (35 miles) altitude, just above
most of Venus' clouds. The polar vortex shows up as an unusually warm
feature at the south pole, surrounded by a collar of colder air. Credit:
ESA / VIRTIS / INAF-IASF / Obs. de Paris-LESIA |
The initial capture orbit was an optimal time to study the south polar vortex
of Venus for several reasons. The initial orbit had a period of nine
days, nearly all of which was spent soaring at distances of greater than 100,000
kilometers (60,000 miles) from the planet's south pole. This gave Venus
Express a continuous view of the spinning vortex. Also, the initial
orbit carried the spacecraft nearly five times the distance from Venus as
its operational orbit would. Closer views permit sharper images, but
this uniquely distant view allowed Venus Express to grab single snapshots
encompassing the entire globe of the planet, something that the VIRTIS instrument
will not be able to repeat throughout the rest of the mission. During
the long sweep of the capture orbit, the science team took six sets of images
and other data. |
Science opportunities from Venus Express' initial orbit
Venus Express' initial orbit lasted nine days, during which there were six
opportunities (or "slots") for the sceince team to test out the spacecraft's
instruments. Credit: ESA / Hâkan Svedhem
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The images below were all captured by VIRTIS during these six opportunities. As
an imaging spectrometer, VIRTIS views of Venus are obtained in hundreds
of wavelengths. Each wavelength penetrates to a different depth
within Venus' 80-kilometer (50-mile) thick atmosphere. Over the
seven days, Venus Express' orbit carried it toward Venus' dayside, so
the planet appears to rotate slightly to the right.
- Ultraviolet/visible (380 nanometers): At this wavelength,
only the dayside of Venus is visible where its uppermost clouds at
an elevation of 80 kilometers (50 miles) reflect incoming sunlight.
Wispy cloud features circle at these high elevations.
- Near infrared (1.7 microns): At this wavelength,
clouds floating at elevations of about 20 to 30 kilometers (12 to 18
miles) block thermal radiation that is emitted from lower in the atmosphere.
The clouds are dark; clear spots through the clouds are bright.
- Thermal infrared (5 microns): At this wavelength,
heat emitted from the upper part of the atmosphere at elevations of
60-80 kilometers (35 to 50 miles) is visible. A polar "dipole" feature
rotates exactly at the south pole.
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April 12, 2006
Range: 210,000 kilometers |
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April 13, 2006
Range: 280,000 kilometers |
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April 14, 2006
Range: 315,000 kilometers |
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April 16, 2006
Range: 315,000 kilometers |
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April 17, 2006
Range: 270,000 kilometers |
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April 19, 2006
Range: 190,000 kilometers |
All images credit: ESA / VIRTIS
/ INAF-IASF / Obs. de Paris-LESIA |
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